Abstract

We have cross-correlated the galaxies from the IRAS 2 Jy redshift survey sample and the 0.7 Jy projected sample with the all-sky cosmic X-ray background (CXB) map obtained from the HEAO 1 A-2 experiment. We have detected a significant correlation signal between surface density of IRAS galaxies and the X-ray background intensity, with W(xg) = {deltaIdeltaN}/{I}{N} of several times 10(-3). While this correlation signal has a significant implication for the contribution of the local universe to the hard (E > 2 keV) X-ray background, its interpretation is model-dependent.We have developed a formulation to model the cross-correlation between CXB surface brightness and galaxy counts. This includes the effects of source clustering and the X-ray-far-infrared luminosity correlation. Using an X-ray flux-limited sample of AGNs, which has IRAS 60 mum measurements, we have estimated the contribution of the AGN component to the observed CXB-IRAS galaxy count correlations in order to see whether there is an excess component, i.e., contribution from low X-ray luminosity sources. We have applied both the analytical approach and Monte Carlo simulations for the estimations.Our estimate of the local X-ray volume emissivity in the 2-10 keV band is rho(x) almost-equal-to (4.3 +/- 1.2) x 10(38) h50 ergs s-1 Mpc-3, consistent with the value expected from the luminosity function of AGNs alone. This sets a limit to the local volume emissivity from lower luminosity sources (e.g., star-forming galaxies, LINERs) to rho(x) less-than-or-similar-to 2 X 10(38) h50 ergs s-1 Mpc-3.

Type:

Article

Title:

THE COSMIC X-RAY-BACKGROUND - IRAS GALAXY CORRELATION AND THE LOCAL X-RAY VOLUME EMISSIVITY